This mod makes some fairly small changes to zombies' behaviors:
* no breaking doors (even on hard mode)
* no pathing through doors, anything in a house gets ignored
* will only target nearby villagers, no hordes of zombies flooding villages all night
As a result, villages are no longer hopelessly overrun by zombies crowding around doors at night and you can play on hard mode, with mobgriefing on, _without_ worrying about doors breaking. At night, zombies tend to just chase loose villagers and then "patrol" around the village.
This may or may not work with mods that add zombie-like mobs.